Since a beat-resistant alloy, such as a Ti alloy and a stainless steel, which is excellent in heat resistance and lightweightness and therefore is often used as a material for a mold and a component, is a difficult-to-cut material, machining efficiency is poor in usual cutting, making it difficult to improve productivity. On the background of this difficulty, there has been developed a cutting tool made of high-hardness material such as a ceramic that allows a high speed cutting of the difficult-to-cut material (see Patent Documents 1 to 5). To ensure the cutting of the difficult-to-cut material at ultrahigh speed, which is higher than a cutting velocity for the high speed cutting, high heat resistance, wear resistance, and strength are required for a material of the cutting tool itself. However, even if the performance is provided to the material itself, cutting ability as the cutting tool fails to be sufficiently exerted is some cases.
For example, a radius end mill or a square end mill has a shape where corner radius edges close to an outer periphery in a radial direction at a distal end of a tool (end mill) or end cutting edges cut a surface of a work material first, and the cutting ability at a center portion on a tool end surface is not expected. Accordingly, the end mill is not suitable for a thrust process where the toot axially advances and a helical process where the tool spirally cuts in the work material in principle. Since a ball end mill is assumed to perform the cutting by the entire cutting edge including the center pan on the tool end surface, the cutting edges may have a configuration of passing through the center on the tool end surface (see Patent Document 6).